Using Distilled or R/O water
Using these types of water in your tank isn't a good idea. After treating it for ammonia, chlorine and chloramine, your city water replenishes calcium and natural mineral buffers that maintain a level pH. Your plants need a continuous source of calcium and other nutrients provided when you do your frequent and large water changes. Distilled and R/O water contain no buffers and can cause sudden changes in the acidity or alkalinity of your tank water.
Just treat your city water and your fish and plants will be fine.
"Fear not my child, just change the tank water."